Add content block type "picture"

[ziegenberg]

Sometimes it is nice to add a picture to the text. For example, you have a page about a certain event, an introductory text and some videos. It would be nice to enrich the text with some pictures about the event. At the moment this is not possible. We would like to upload a picture which is then saved in Tobira. It should be able to handle all common picture formats (JPG, PNG, AVIF, WebP).